Angiotensin II (A-II) has been reported to be present within the central nervous system and to exert effects on blood pressure, vasopressin release and water/electrolyte balance. Preliminary data is presented which confirms its presence in the rat hypothalamus by both radioimmunoassay (RIA) and immunocytochemistry. This proposal is designed to first identify and characterize this central A-II like peptide using a combination of high pressure liquid chromatography (HPLC, for separation of small polypeptides) and immunological techniques. This will include in vitro hypothalamic biosynthetic studies to determine whether A-II is synthesized de novo within the tissue or merely sequestered from exogenous sources. An investigation into the interactions of A-II and vasopressin in the etiology of spontaneous hypertension is also proposed. Acute and chronic physiological experiments are planned to determine the effect of intraventricular A-II or its antagonists on blood pressure, vasopressin secretion, and fluid/electrolyte balance in the conscious unrestrained rat. In addition, endogenous brain levels of A-II and vasopressin will be localized and quantitated using both RIA and immunocytochemistry. Thus, the primary purpose of this investigation is to further characterize the brain angiotensin axis and to investigate its possible role in the pathogenesis of hypertension.